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Doubts cast over HRT link to breast cancer


January 17, 2012 - London

Doubts have been raised over hormone replacement therapy's role in increasing breast cancer risk, with researchers claiming that raised fears were 'fundamentally flawed'.

The million women study indicated that women taking HRT were twice as likely to develop breast cancer and more likely to die from it than those not taking the therapy.

The study, funded by Cancer Research UK and conducted by a team at Oxford University, resulted in a collapse of confidence in hormone replacement therapy and the number of women taking it halved.

Several studies later showed a small increased risk of cancer and a fierce debate has raged over the issue.

In 2002, before the Million Women Study reported there were 4.9m prescriptions dispensed in England for the treatment, compared with 2.3m last year.

However, a new analysis of the study and two others, found that it cannot prove that the treatment causes an increased risk of developing breast cancer, experts said.

The researchers have maintained that there were several flaws in the study including that women may have already had breast cancer when they were enrolled in the study and that they were at increased risk of dying within three years which was 'biologically implausible'.

"The name 'Million Women Study' implies an authority beyond criticism or refutation," the Telegraph quoted Prof Samuel Shapiro from the University of Cape Town and others as saying.

"Here we conclude that the evidence in the Million Women Study was indeed unreliable. There were defects in the study design, and the findings did not adequately satisfy the principles of causation.

"HRT may or may not increase the risk of breast cancer but the Million Women Study did not establish that it does."

The authors also claimed that inviting women to join the study would in itself have increased the number already aware of breast lumps or precancerous changes, leading to higher numbers of cancers being detected (detection bias).

The authors also disputed that crucial data was often also missing.

"Yet the validity of any study is dependent on the quality of its design, execution, analysis and interpretation. Size alone does not guarantee that the findings are reliable," Prof Shapiro wrote.

"The Million Women Study was an observational study, and it has the attendant problems and uncertainties intrinsic to such studies.

"If the evidence was unreliable, the only effect of its massive size would have been to confer spurious statistical authority to doubtful findings."

According to Dr Susie Jennings, Senior Policy Officer at Breakthrough breast cancer, many studies have revealed that HRT increases the risk of breast cancer and this study does not change that.

"It does suggest the risks may, in some instances, have been slightly overstated," Dr Jennings said.

The study has been published in the Journal of Family Planning and Reproductive Health Care.

ANI

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